More than 780,000 votes were cast by Sunday, the final day of an unofficial referendum on democratic reforms in Hong Kong, part of a civil campaign that has been branded illegal by local and mainland Chinese authorities.

Hong Kong, a free-wheeling, capitalist hub of more than seven million people, returned to Chinese rule in 1997 with wide-ranging autonomy under a “one country, two systems” formula, along with an undated promise of universal suffrage.

While Beijing says Hong Kong can go ahead with a vote in 2017 for the city’s top leader, Hong Kong’s mini-constitution, the Basic Law, specifies that only a nominating committee can pick leadership candidates.

Democracy activists want the nomination process to be open to everyone, in line with international standards, and have threatened to lock down the Central area of Hong Kong, home to some of Asia’s biggest companies and banks, if the city fails to adopt a strong democratic method for electing its next leader.

“I think the signal has already been sent to Beijing that Hong Kong people are prepared to express their views on universal suffrage,” said Benny Tai, associate professor of law at the University of Hong Kong and one of the organisers of the vote and the movement, Occupy Central with Love and Peace. “We hope the result of the civil referendum will be taken seriously by the SAR (Special Administrative Region of Hong Kong) and Chinese government.”

The unofficial vote, organised by pro-democracy activists, has been conducted mainly online. Voters are required to give their identification number to prevent cheating.

At a “polling booth” at Chinese University of Hong Kong on Sunday, a small group of pro-Beijing supporters with mainland accents held up banners denouncing the vote, while four people jumped into the city’s Victoria Harbour to protest against the referendum and were quickly rescued.

Another pro-Beijing group, Caring Hong Kong Power, marched through the busy shopping district of Causeway Bay carrying bright orange balloons and urging people not to vote. Group spokeswoman Lee Ka-ka handed a petition to police signed by 30,000 against the Occupy Central group. She also urged police to “act strongly against the movement”.